I can see your plan.
In similar situations I have allowed my car, with the ICE off, to roll if there is a little gradient, or where the law allows and I have been standing beside my car getting some air I just push it a little once in a while.
Unless you have the need to do that very often I am not sure how worthwhile it would be to have a system attached to the car to do that.
If the wheels of the device are on the road then they will need to be able to spin up to the full speed of the car otherwise they will need a method for raising and lowering them to the road surface.
You could look at those trailer movers used at camp and caravan sites, a pair of driven wheels with a tow ball on top. Maybe one of those could be adapted to the task.
There are also motors to drive the wheels, that could work.
I can imagine, if it is a front engine rear wheel drive car then a motor on the propshaft/driveshaft to the rear axle would be an easier proposition.
An Agni95R may be able to spin up to the high speed needed and present little drag and weight when not in use. It would draw high current to move the car at low speed though.
Alternatively a geared motor doing the same job would draw less current moving the car but it would need a freewheel, or sprag clutch, to prevent it from being overspeeded by the propshaft. That would mean no high speed reversing though.
Maybe a motor with a loose belt drive to the tail shaft of the trans or the nose of the diff. The belt tension could be pulled tight with a lever or pneumatic cylinder when drive was needed.
This is all getting a little away from the EV scene though, but still an interesting idea.
Do check the legality issues where you are, just in case there are any issues.
Maybe more ICE car manufacturers should have low power electric drive for maneuvering and parking as a matter of course. I'd like it as an option.